Not all Essential Oils are created equal. That is an understatement if you ask me. Not only are essential oils dependant on the soil, the nutrients, the water, but also the way they are extracted and stored.
There are several different essential oil extraction methods that create different types of oils from the same plant.
In this article I want to go over each method with you, what the benefits are to each method, and why we use oils from the CO2 Extraction Method. If you want to start at teh basics, read our article on Essential Oils 101
This method was used to extract essences from the citrus family. The rinds of the fruit were literally squeezed by hand until the oil glands burst releasing the oil which was then collected in a sponge. Once saturated, the sponge would be squeezed out into a container.
Nowadays, this method of extraction is carried out using machinery, rather than by hand.
Another historical method used for extracting essential oil from flowers is the process of ‘enfleurage’.
Aromatic flower heads are placed on sheets of glass called ‘chassis’ which have been covered with purified fat. The fat absorbs the essential oils from the flowers and, once exhausted, the flowers are removed and replaced with fresh. This process is repeated many times until the fat is saturated with essential oil. The resultant compound is called a ‘pomade’. The pomade is then dissolved in alcohol. Fat is insoluble in alcohol but essential oil readily dissolves into it. The resultant liquid is then carefully heated and as the alcohol evaporates first, the pure essential oil is left behind.
This process is similar to enfleurage and is a method by which one can still make essential oil at home in a ready diluted state.
The flowers or leaves are crushed to rupture some of the oil glands or cells and then put into a vegetable oil which is kept warm. The vegetable oil absorbs the essential oil and the plant material is strained off. Fresh plant material is then added to the re-warmed carrier and this process is repeated until the fat or vegetable oil is concentrated enough.
Chemical Solvent Extraction
This is one of the most modern methods of extraction and is mainly used for costly and delicate flower oils, such as jasmine, rose and tuberose, etc. Technically, products of solvent extraction are not essential oils, but are more accurately referred to as ‘absolutes’.
Unfortunately though, solvent extraction does involve the use of harsh chemicals, residues of which will inevitably remain within the aromatic absolute, resulting in potential skin irritation. As such, absolutes are not considered to be suitable for use in massage.
A simplified version of the solvent extraction process is as follows:
- Firstly, the flowers are covered with a chemical solvent, which absorbs the essential oil. The mixture of solvent and essential oil is referred to as an ‘extract’.
- The next stage involves the removal of the solvent and this is achieved by distilling the extract at a low pressure, thereby reducing the boiling point of the solvent, so that only gentle heat is required to remove it, leaving behind the aromatic molecules.
- The concentrated extract is then cooled causing it to solidify to a waxy consistency – at this point it is referred to as a ‘concrete’.
- In order to remove the unwanted wax, the concrete is ‘washed’ and warmed in alcohol which causes the oils to dissolve into it.
- The alcohol mixture is then chilled to separate out any remaining waxes, filtered and the alcohol is removed by vacuum distillation at the lowest possible temperature. This final product is then referred to as an ‘absolute’.
Carbon Dioxide (CO2) Extraction (our fav)
CO2 extraction is a relatively recent development over the last few decades. It produces oils that are very pure and with a unique quality, such that they can differ greatly from steam distilled essential oils. Other advantages include the fact that CO2 is inert which means that it does not react chemically with the oil being extracted. It is non-toxic, colorless and odorless, temperatures are kept very low, so thermally labile compounds do not suffer damage; there are no ‘still’ notes and more top notes; the true natural odor and flavor characteristics are retained.
Basically, carbon dioxide can take the form of either a liquid or gaseous state depending upon the atmospheric pressure and temperature it is subjected to. At above 33°C and over 200 atmospheres (i.e., 200 times that of regular atmospheric pressure), CO2 reaches a ‘hypercritical state’, i.e., it is too hot to be a conventional liquid, and too pressurized to be a conventional gas (i.e., it is at the tipping point between). As such, it can be widely dispersed amongst the charge and have solvent properties. Hypercritical CO2 extraction allows for the production of oils at low temperatures and very quickly (i.e., just a few minutes), with no chemical residue attached to the final product. Once extraction is complete, the pressure is released and the carbon dioxide returns to its gaseous state, leaving behind the whole oil.
Because the extraction process takes place in a completely sealed chamber, the whole oil is recovered, including the most volatile and fragile components. However, this has a downside, in that the concentration of pesticide residues from the original plant material, are considerably greater than the values obtained by other more conventional methods of extraction. CO2 extraction really does recover everything from the plant material.
In order to isolate essential oils by hydrodistillation, the aromatic plant material is packed in a still and a sufficient quantity of water is added and brought to a boil; alternatively, live steam is injected into the plant charge. Due to the influence of hot water and steam, the essential oil is freed from the oil glands in the plant tissue. The vapor mixture of water and oil is condensed by indirect cooling with water. From the condenser, distillate flows into a separator, where oil separates automatically from the distillate water. Mechanism of Distillation Hydrodistillation of plant material involves the following main physicochemical processes:
- i) Hydrodiffusion
- ii) Hydrolysis
- iii) Decomposition by heat
Hydrodiffusion involves the diffusion of essential oils and hot water through plant membranes. In steam distillation, the steam does not actually penetrate the dry cell membranes. Therefore, dry plant material can be exhausted with dry steam only when all the volatile oil has been freed from the oil-bearing cells first, thorough comminution of the plant material. However, when the plant material is soaked with water, exchange of vapors within the tissue is based on their permeability while in a swollen condition. Membranes of plant cells are almost impermeable to volatile oils. Therefore, in the actual process, at the temperature of boiling water, a part of volatile oil dissolves in the water present within the glands, and this oil-water solution permeates, by osmosis, the swollen membranes and finally reaches the outer surface, where the oil is vaporized by passing steam. Another aspect of hydrodiffusion is that the speed of oil vaporization is not influenced by the volatility of the oil components, but by their degree of solubility in water. Therefore, the high-boiling but more water-soluble constituents of oil in plant tissue distill before the low-boiling but less water-soluble constituents. Since hydrodiffusion rates are slow, distillation of uncomminuted material takes longer time than comminuted material.
There are several other kids of essential oil extraction methods but these are the main ones that have been used throughout history and into today. We use CO2 extraction oils as well as low hydrodistillation oils – for their purity and potency.